Method for encrypting content, method for decrypting content and electronic apparatus applying the same

ABSTRACT

A method for encrypting content includes using a plurality of different encryption schemes to produce encrypted content. Encryption information is provided so as to indicate which of the plurality of different encryption schemes is used on portions of the content that was encrypted. Encryption information and the encrypted content are both sent as a content stream to another device. The decryption involves using the encryption information to help control the decryption so that the correct one of a plurality of different decryption schemes is applied to the proper portions of the encrypted content.

TECHNICAL FIELD

The inventive concept relates to a method for encrypting, a method fordecrypting, and an electronic apparatus applying the same. Moreparticularly, the inventive concept relates to a method for encryptingand transmitting content and a method for decrypting and reproducing areceived content.

DESCRIPTION OF RELATED ART

Since the image quality and the sound quality of digital content doesnot deteriorate even if the digital content is copied, and also sincedigital content is easy to copy, the copyright on digital content isfrequently infringed.

To prevent the unauthorized copying of digital content, variousencryption technologies have been developed. To counter this, however,the technology to hack the key used to encrypt/decrypt digital contenthas also been developed; the unauthorized copying of digital content hastherefore not been fully prevented.

Accordingly, there is a demand for a method of providing strongerprotection of digital content against unauthorized copying. Also, suchprotection should be achieved by a method for reinforcing a means forencrypting digital contents and a method for reinforcing a means forauthenticating an apparatus which requests digital contents.

DETAILED DESCRIPTION

The inventive concept has been developed to help solve or ameliorate theabove problems. One or more of the exemplary embodiments may include amethod for complex encryption of content by the complex application of aplurality of encrypting schemes to selected digital content, as a methodfor reinforcing a means for encrypting digital contents.

Also, one or more of the exemplary embodiments may include a method forthe complex decryption of content which has been encrypted by thecomplex application of a plurality of encrypting schemes, as describedabove.

In addition, one or more of the exemplary embodiments may include amethod for updating a hacked key list that is stored in an apparatuswith reference to a hacked key list stored in a different externalapparatus, as a method for reinforcing a means for authenticating anapparatus which requests digital contents.

According to an aspect of an exemplary embodiment, there is provided amethod for encrypting content, the method including: complex encryptionby the complex application of a plurality of encrypting schemes toselected content, and adding encryption information to the content whichis encrypted by the complex application of a plurality of encryptingschemes in the complex encryption operation.

The complex encryption may include the complex application of theplurality of encrypting schemes on at least one of a frame basis, afield basis, and a line basis.

The plurality of encrypting schemes may include a high bandwidth digitalcontent protection XOR (HDCP-XOR) encrypting scheme and an HDCP-XNORencrypting scheme.

The adding of the encryption information may include: 1) if the contentis encrypted on the frame basis, adding the encryption information toevery frame, 2) if the content is encrypted on the field basis, addingthe encryption information to every field, and 3) if the content isencrypted on the line basis, adding the encryption information to everyline.

The method may further include: authenticating a connected apparatus,and transmitting a content stream, including the content that has beenencrypted in a complex manner, and also including the encryptioninformation, to the connected apparatus, and the complex encryption maybe performed if the authentication succeeds.

The method may further include updating a hacked key list which isreferred to in authenticating the connected apparatus.

The updating may include: receiving a hacked key list of a connectedexternal apparatus from the external apparatus, and adding to the hackedkey list a hacked key that is recorded on the hacked key list of theexternal apparatus but does not exist in the hacked key list.

The hacked key list may be received from one of a network, a broadcastsignal, a storage medium, and content stored in a storage medium.

According to an aspect of another exemplary embodiment, there isprovided an electronic apparatus including: an encryption unit whichcarries out complex encryption by the complex application of a pluralityof encrypting schemes to selected content, and an encoding unit whichadds encryption information to the content which is encrypted by theencryption unit as mentioned above.

According to an aspect of still another exemplary embodiment, there isprovided a method for decrypting content, the method including:receiving content which has been encrypted by the complex application ofa plurality of encrypting schemes to the content, and decrypting theencrypted content using a plurality of decrypting schemes with referenceto encryption information added to the encrypted content.

The complex encryption may include the complex application of theplurality of encrypting schemes on at least one of a frame basis, afield basis, and a line basis, and the complex decryption may includethe complex application of the plurality of decrypting schemes on atleast one of the frame basis, the field basis, and the line basis.

The plurality of encrypting schemes may include an HDCP-XOR encryptingscheme and an HDCP-XNOR encrypting scheme, and the plurality ofdecrypting schemes may include an HDCP-XOR decrypting scheme and anHDCP-XNOR decrypting scheme.

The encryption information may be referred to every frame if the contentwas decrypted on a frame basis. The encryption information may bereferred to every field if the content was decrypted on a field basis.The encryption information may be referred to every line if the contentwas decrypted on the line basis.

According to an aspect of still another exemplary embodiment, there isprovided an electronic apparatus including: a communication unit whichreceives content that was encrypted by the application of a plurality ofencrypting schemes to selected content, a decryption unit which decryptsthe thus-encrypted content using a plurality of decrypting schemes, anda controller which controls the decrypting operation of the decryptionunit with reference to encryption information added to the encryptedcontent.

According to an aspect of still another exemplary embodiment, there isprovided a method for updating a hacked key list of an electronicapparatus, the method including: at the electronic apparatus, receivingfrom an external apparatus a hacked key list stored in the externalapparatus, and, at the electronic apparatus, updating a hacked key liststored in the electronic apparatus using the hacked key list received inthe receiving operation.

The updating may include adding a hacked key, that is recorded on thehacked key list of the external apparatus, but does not exist in thehacked key list stored in the electronic apparatus, to the hacked keylist of the electronic apparatus.

The method may further include, at the electronic apparatus,transmitting the hacked key list stored in the electronic apparatus tothe external apparatus.

The hacked key list may be a hacked B key selection vector (BKSV) list.

The updating may be performed in any one of the following cases, 1)periodically, 2) when the external apparatus is connected, or 3) whenthere is a change in the hacked key list stored in the externalapparatus.

The receiving may include receiving the hacked key list from one of anetwork, a broadcast signal, a storage medium, and content stored in astorage medium.

As described above, since the content is encrypted by the complexapplication of the plurality of encrypting schemes to the signalcontent, a means for encrypting digital contents can be reinforced. Thatis to say, the protection for digital content is strengthened.

Also, since the hacked key list stored in the electronic apparatus isupdated with reference to the hacked key list stored in another externalapparatus, or by receiving the hacked key list from the connectednetwork, the broadcast signal, the storage medium, or the content storedin the storage medium, a means for authenticating an apparatus whichrequests digital contents can be reinforced. That is to say, the processfor apparatus authentication is strengthened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a home network to which the inventiveconcept is applicable;

FIG. 2 is a block diagram illustrating a source apparatus of FIG. 1;

FIG. 3 is a flowchart to explain a method for encrypting a contentaccording to an exemplary embodiment;

FIG. 4 is a block diagram illustrating a sink apparatus of FIG. 1;

FIG. 5 is a flowchart to explain a method for decrypting a contentaccording to another exemplary embodiment; and

FIG. 6 is a flowchart to explain a method for updating a hacked B keyselection vector (BKSV) list according to still another exemplaryembodiment.

DETAILED DESCRIPTION

Hereinafter, the inventive concept will now be described in greaterdetail with reference to the accompanying drawings.

1. Configuration of Home Network

FIG. 1 is a view illustrating a home network to which the inventiveconcept is applicable. The home network is established so that a set topbox (STB) 100-1, a digital versatile disk player (DVDP) 100-2, a digitaltelevision (DTV)-1 200-1 and a DTV-2 200-2 communicate with one another.

More specifically, the STB 100-1 is communicably connected to the DTV-1200-1 and the DTV-2 200-2 through a high definition multimedia interface(HDMI), and the DVDP 100-2 is also communicably connected to the DTV-1200-1 and the DTV-2 200-2 via HDMI.

Each of the STB 100-1 and the DVDP 100-2 may be understood to constitutea source apparatus that provides content. Each of the DTV-1 200-1 andthe DTV-2 200-2 may be understood to constitute a sink apparatus thatreceives the content.

Hereinafter, detailed configurations of a source apparatus and a sinkapparatus will be explained. First, each of the STB 100-1 and the DVDP100-2 will be referred to as a source apparatus and will be explained indetail with reference to FIG. 2.

2. Source Apparatus and Method for Encrypting Content

As shown in FIG. 2, a source apparatus 100 includes a content obtainer110, a content encryption unit 120, an encoding unit 130, a sourcecommunication unit 140, a source controller 150, and a source memory160.

The content obtainer 100 obtains content from a content source andprovides the content to the content encryption unit 120. The contentobtainer 110 may obtain the content in different ways according to thetype of the source apparatus 100.

For example, 1) if the source apparatus 100 is the STB 100-1, thecontent obtainer 110 obtains content by receiving it from a broadcastingstation through a cable or an antenna; 2) if the source apparatus 100 isthe DVDP 100-2, the content obtainer 110 obtains content by reading outit from a DVD.

The content encryption unit 120 performs complex encryption on thecontent output from the content obtainer 110 using a high bandwidthdigital content protection XOR (HDCP-XOR) encryption module 121 and anHDCP-XNOR encryption module 123. As a result, the content encryptionunit 120 outputs the complex encrypted content. A method for carryingout the complex encryption of the content will be explained in detailbelow.

The details of the complex encryption performed by the contentencryption unit 120 are carried out under the control of the sourcecontroller 150.

The encoding unit 130 adds encryption information and other necessaryinformation, to the content encrypted in a complex manner by the contentencryption unit 120, thereby generating a content stream. The encryptioninformation may be recorded on a blanking section and may be transmittedalong with the blanking section, or may be transmitted through aseparate communication channel.

The encryption information is information about the details of thecomplex encryption performed by the content encryption unit 120 and iscreated by the source controller 150. This is because that the detailsof the complex encryption performed by the content encryption unit 120are under the control of the source controller 150.

The source communication unit 140 transmits the content stream generatedby the encoding unit 130 to a sink apparatus 200.

The source controller 150 controls the content obtaining operation ofthe content obtainer 110, the complex encrypting operation of thecontent encryption unit 120, the content stream generating operation ofthe encoding unit 130, and the content stream transmitting operation ofthe source communication unit 150.

Also, the source controller 150 authenticates the sink apparatus 200connected through the source communication unit 140. Also, the sourcecontroller 150 updates a hacked B key selection vector (BKSV) list whichis stored in the source memory 160 to be used to authenticate,separately from the authenticating operation.

Specifically, if the sink apparatus 200 transmits its own hacked BKSVlist to the source apparatus 100, the source controller 150 compares thehacked BKSV list, which is received from the sink apparatus 200, and thehacked BKSV list which is stored in the source memory 160. If the listsare not identical, the source controller 150 updates the hacked BKSVlist by adding any hacked BKSV that is not present in the hacked BKSVlist of the source apparatus 100.

Hereinafter, a method for encrypting content using the source apparatus100 of FIG. 2 will be explained, in detail, with reference to FIG. 3.FIG. 3 is a flowchart illustrating a method for encrypting contentaccording to an exemplary embodiment.

As shown in FIG. 3, the source controller 150 authenticates the sinkapparatus 200 which is connected through the source communication unit140 (S310). The authenticating process performed in operation S310 is asdescribed below.

First, the source controller 150 determines whether a BKSV received fromthe sink apparatus 200 is a hacked BKSV or not. Since a hacked BKSV listis stored in the source memory 160, the source controller 150 refers tothe hacked BKSV list. If it is determined that the BKSV received fromthe sink apparatus 200 is a hacked BKSV, the authentication fails.

Next, the source controller 150 determines whether R₀′ generated basedon an A key selection vector (AKSV) and A_(n) is identical to R₀received from the sink apparatus 200 along with the BKSV. The AKSV andA_(n) are generated by the source controller 150 using an HDCP key andR₀ is generated by the sink apparatus 200. If R₀′≠R₀, the authenticationfails.

If the BKSV received from the sink apparatus 200 is not a hacked BKSVand if R₀′=R₀, the authentication succeeds.

If the authentication succeeds (5320-Y), the source controller 150controls the content encryption unit 120 to perform complex encryptionwith respect to the content output from the content obtainer 110 (S330).

The term “complex encryption” refers to a method for encrypting a singlecontent using two encrypting schemes. The complex encryption may berealized in various ways and will be explained in detail below.

First, the complex encryption may be applied on a per-frame basis. Thecontent may consist of frames. More specifically, the complex encryptionis performed by 1) performing HDCP-XOR with respect to specific framesamong the frames that form the content, using the HDCP-XOR encryptionmodule 121, and then 2) performing HDCP-XNOR encryption with respect tothe remaining frames, using the HDCP-XNOR encryption module 123.

Second, the complex encryption may be applied on a per-field basis. Thecontent may consist of fields. Specifically, the complex encryption isperformed by 1) performing the HDCP-XOR encryption with respect tospecific fields among the fields that form the content, using theHDCP-XOR encryption module 121, and then 2) performing the HDCP-XNORencryption with respect to the remaining fields using the HDCP-XNORencryption module 123.

Third, the complex encryption may be applied on a per-line basis. Theframe or the field of the content may consist of lines. Specifically,the complex encryption is performed by 1) performing the HDCP-XORencryption with respect to specific lines among the lines that form theframe or the field of the content, using the HDCP-XOR encryption module121, and then 2) performing the HDCP-XNOR encryption with respect to theremaining lines using the HDCP-XNOR encryption module 123.

Fourth, the complex encryption may be performed by combining two or moreof the above-described three ways.

After that, the source controller 150 controls the encoding unit 130 togenerate a content stream by adding encryption information to thecontent encrypted in the above-described complex manner in operation5330 (S340).

The encryption information is a record of information about theencrypting schemes (HDCP-XOR encryption or HDCP-XNOR encryption) used tocreate the content recorded on the content stream to which theencryption information belongs.

Accordingly, 1) if the complex encryption is performed on the per-framebasis, the encryption information should be added to every frame,

2) if the complex encryption is performed on the per-field basis, theencryption information should be added to every field, and

3) If the complex encryption is performed on the per-line basis, theencryption information should be added to every line.

Regardless of which basis is used for the encryption, the encryptioninformation may be added to every line. If the encryption information isadded to every line, the decryption may be performed with reference tothe encryption information regardless of whether the encryption isperformed on the per-frame basis, the per-field basis, or the per-linebasis, since the line is the smallest unit.

After that, the source communication unit 140 transmits the contentstream generated in operation 5340 to the sink apparatus 200 (S350).

If the authentication fails in operation 5310 (S320-N), operations 5330to 350 are not performed. That is, the source apparatus 100 does nottransmit the content to the sink apparatus 200.

3. Sink Apparatus and Method for Decrypting Content

Hereinafter, the DTV-1 200-1 and the DTV-2 200-2 will be referred to asexamples of a sink apparatus 200 and will be explained with reference toFIG. 4.

As shown in FIG. 4, the sink apparatus 200 includes a sink communicationunit 210, a decoding unit 220, a content decryption unit 230, a contentoutput unit 240, a sink controller 250, and a sink memory 260.

The sink communication unit 210 receives a content stream from thesource communication unit 140 of the source apparatus 100 and transmitsthe content stream to the decoding unit 220.

The decoding unit 220 decodes the content stream received, through thesink communication unit 210, from the source apparatus 100. The contentstream includes the complex, encrypted content and the encryptioninformation. The decoding unit 220 extracts from the content stream thecomplex, encrypted content, and extracts the encryption information. Theencrypted content is sent to the content decryption unit 230 and theencryption information is sent to the sink controller 250.

The content decryption unit 230 decrypts the content transmitted fromthe decoding unit 220 using an HDCP-XOR decryption module 231 and anHDCP-XNOR decryption module 233. As a result, the content decryptionunit 230 outputs the decrypted content.

The sink controller 250 controls the decrypting operation of the contentdecryption unit 230 based on the encryption information transmitted fromthe decoding unit 220.

The content output unit 240 outputs the content thus decrypted by thecontent decryption unit 230 and provides the content for the user. Thecontent is output by the content output unit 240 in different ways inaccordance with the type of the sink apparatus 200.

For example, if the sink apparatus 200 is the DTV 200-1 or 200-2, thecontent output unit 240 outputs the content through a display.

The sink controller 250 controls the content stream receiving operationof the sink communication unit 210, the decoding operation of thedecoding unit 220, the complex decryption operation of the contentdecryption unit 230, and the content outputting operation of the contentoutput unit 240.

The sink controller 250 performs an authentication process with respectto the source apparatus 100 connected through the sink communicationunit 210. The sink controller 250 updates a hacked BKSV list which isstored in the sink memory 260 to be used to authenticate, separatelyfrom the previously mentioned authenticating operation.

More specifically, if the source apparatus 100 transmits its own hackedBKSV list to the sink apparatus 200, the sink controller 250 comparesthe hacked BKSV list received from the source apparatus 100 with thehacked BKSV list stored in the sink memory 260. If the lists are notidentical, the sink controller 250 updates the BKSV list of the sinkapparatus 200 by adding to it the hacked BKSV from the source apparatus100 that is missing from the BKSV list of the sink apparatus 200.

Hereinafter, a method for decrypting the content from the sink apparatus200 shown in FIG. 4 will be explained with reference to FIG. 5. FIG. 5is a flowchart illustrating a method for decrypting the contentaccording to another exemplary embodiment.

As shown in FIG. 5, the sink controller 250 performs an authenticatingprocess with respect to the source apparatus 100, which is connectedthrough the sink communication unit 210 (S410). The authenticatingprocess in operation S410 is the same as in operation S310 of FIG. 3.

If the authentication succeeds (S420-Y), the sink communication unit 210receives the content stream from the source apparatus 100 (S430). Thecontent stream received in operation S430 is the content streamtransmitted in operation S350 of FIG. 3.

The content stream includes the encrypted content and the encryptioninformation. The encrypted content is the content that was generated inoperation S330 of FIG. 3, and the encryption information is theinformation that was added to the encrypted content in operation S340 ofFIG. 3.

The decoding unit 220 decodes the content stream received in operationS430 and extracts the encrypted content and the encryption information(S440). The encrypted content extracted in operation S440 is transmittedto the content decryption unit 230; the encryption information istransmitted to the sink controller 250.

The sink controller 250 controls the content decryption unit 230 toperform complex decryption with respect to the encrypted contentextracted in operation S440 based on the encryption informationextracted in operation S440 (S450).

The complex decryption is an inverse operation of the complex encryptionand is a method for decrypting a single content using two decryptingschemes. The complex decryption is performed based on the encryptioninformation that was transmitted along with the encrypted content.

For example, in the case that the content is encrypted on the per-framebasis,

1) if it is determined that the frame is an HDCP-XOR encrypted frame,based on the encryption information, the sink controller 250 controlsthe content decryption unit 230 to decrypt the frame using the HDCP-XORdecryption module 231, and

2) if it is determined that the frame is an HDCP-XNOR encrypted frame,based on the encryption information, the sink controller 250 controlsthe content decryption unit 230 to decrypt the frame using the HDCP-XNORdecryption module 233.

After that, the content output unit 240 outputs the content, which hasbeen decrypted, in operation 5450 and then provides the content to theuser (S460).

If the authentication fails in operation 5420 (S420-N), operations 5430to S460 are not performed. This is because the content stream is nottransmitted from the source apparatus 100 if the authentication fails.

4. Method for Sharing Hacked BKSV of Home Apparatus

The source apparatus 100 and the sink apparatus 200 have a commonfeature in that they are home apparatuses. Hereinafter, a process ofsharing a hacked BKSV list among the home apparatuses will be explainedwith reference to FIG. 6. FIG. 6 is a flowchart illustrating a methodfor updating a hacked BKSV list according to still another exemplaryembodiment.

As shown in FIG. 6, if a home apparatus 100 or 200 is connected toanother home apparatus through the communication unit 140 or 210(S510-Y), the controller 150 or 250 transmits a hacked BKSV list storedin the memory 160 or 260 to the other home apparatus (S520).

The controller 150 or 250 receives the hacked BKSV list from anotherhome apparatus through the communication unit 140 or 210 (S530).

The controller 150 or 250 updates its own hacked BKSV list, stored inthe memory 160 or 260, with reference to the hacked BKSV list of theother home apparatus, which was received in operation S530 (S540).

More specifically, the controller 150 or 250 adds a hacked BKSV that isrecorded on the hacked BKSV list of the other home apparatus, but is notin the hacked BKSV list of the home apparatus 100 or 200, to the hackedBKSV list of the home apparatus 100 or 200.

The hacked BKSV list may be updated 1) periodically, 2) if another homeapparatus is connected, or 3) if there is a change in the hacked BKSVlist of the one home apparatus 100 or 200 or in the hacked BKSV list ofthe other home apparatus. The hacked BKSV list is not necessarily sharedonly between a source apparatus and a sink apparatus. The hacked BKSVlist may be shared among the source apparatuses, for example, or may beshared among the sink apparatuses. For example, the hacked BKSV list maybe shared between the STB 100-1 and the DVDP 100-2, which are the sourceapparatuses in the home network of FIG. 1. Also, the hacked BKSV listmay be shared between the STB 100-1 or the DVDP 100-2 and the DTV-1200-1 or may be shared between the STB 100-1 or DVDP 100-2 and the DTV-2200-2 in the home network of FIG. 1. Accordingly, the DTV-1 200-1 andthe DTV-2 200-2 can share the hacked BKSV list by the media of the STB100-1 or the DVDP 100-2.

The method for updating the hacked BKSV list is not necessarily carriedout if the connection is made through an HDMI or a DVI. The hacked BKSVlist may alternatively be updated by receiving a hacked BKSV list from anetwork in which apparatuses are connected to one another, from abroadcast signal, form a storage medium, or from a content stored in thestorage medium.

For example, the hacked BKSV list may be updated by 1) receiving ahacked BKSV list from a server connected through a network, 2) receivinga hacked BKSV list recorded on a certain area of a broadcast signal, or3) reading out a hacked BKSV list from a medium such as a BD, a DVD, aCD and a memory or from content stored in the medium.

5. Variations

The home network mentioned above is merely an example of a network. Theinventive concept is applicable to a network other than the homenetwork. Also, although the home apparatuses forming the home networkare in this example connected to one another through the HDMI, it doesnot matter which connecting method is used in applying the inventiveconcept. Accordingly, the home apparatuses may be connected to oneanother in a method other than using HDMI.

The home apparatuses mentioned above are merely examples for convenienceof explanation. The inventive concept is applicable to any otherelectronic apparatus.

Also, the encrypting schemes and the decrypting schemes are merelyexamples. They may be replaced with other schemes. Also, three or moreencrypting schemes may be applied in a complex manner and three or moredecrypting schemes may be applied in a complex manner.

Also, the hacked BKSV list is merely an example of a hacked key list.Accordingly, another kind of hacked key list may be used and updated.

The foregoing exemplary embodiments and advantages are merely examplesand are not to be construed as limiting the present inventive concept.The exemplary embodiments can be readily applied by analogy to othertypes of apparatuses. Also, the description of the exemplary embodimentsis intended to be illustrative, and not to limit the scope of theclaims. Many alternatives, modifications, and variations will beapparent to those skilled in the art.

The invention claimed is:
 1. A method for encrypting content, the methodcomprising: encrypting by using a plurality of different encryptingschemes to a single content to provide encrypted content; and addingencryption information to the encrypted content; wherein the encryptioninformation indicates ones of the plurality of different encryptingschemes for subsequent use in decrypting corresponding portions of theencrypted content, and wherein the content is encrypted after anauthentication to a connected apparatus succeeds, wherein the singlecontent comprises a plurality of frames, each frame comprises aplurality of fields, and each frame or each field comprises a pluralityof lines, wherein the encrypting comprises performing encryption byapplying a first encryption method to a first line and a secondencryption method to a second line through the remaining lines among thelines which form the frame or field, and wherein the adding encryptioninformation comprises adding first information indicating the firstencryption method which is used in the first line to the first line andadding second information indicating the second encryption method whichis used in the second line to the second line.
 2. The method as claimedin claim 1, wherein the encrypting comprises applying the plurality ofdifferent encrypting schemes on at least one of a per-frame basis, aper-field basis, and a per-line basis.
 3. The method as claimed in claim2, wherein the plurality of different encrypting schemes comprise a highbandwidth digital content protection (HDCP)-XOR encrypting scheme and anHDCP-XNOR encrypting scheme.
 4. The method as claimed in claim 2,wherein the adding of the encryption information comprises: 1) when thecontent is encrypted on the per-frame basis, adding the encryptioninformation to every frame; 2) when the content is encrypted on theper-field basis, adding the encryption information to every field; and3) when the content is encrypted on the per-line basis, adding theencryption information to every line.
 5. The method as claimed in claim1, further comprising: authenticating a connected apparatus; andtransmitting a content stream comprising the encrypted content and theencryption information to the connected apparatus.
 6. The method asclaimed in claim 5, further comprising updating a hacked key list usedin authenticating the connected apparatus.
 7. The method as claimed inclaim 6, wherein the updating comprises: receiving a hacked key listfrom the connected external apparatus; and when a hacked key in thehacked key list from the connected external apparatus is not in a storedhacked key list, updating the stored hacked key list to include thehacked key from the connected external apparatus.
 8. An electronicapparatus comprising: an encryption unit which encrypts by using aplurality of different encrypting schemes to a single content to provideencrypted content; and an encoding unit which adds encryptioninformation to the encrypted; wherein the encryption informationindicates ones of the plurality of different encrypting schemes forsubsequent use in decrypting corresponding portions of the encryptedcontent, wherein the encryption unit encrypts the content after anauthentication to a connected apparatus succeeds, wherein the singlecontent comprises a plurality of frames, each frame comprises aplurality of fields, and each frame or each field comprises a pluralityof lines, wherein the encryption unit encrypts by applying a firstencryption method to a first line and a second encryption method to asecond line through the remaining lines among the lines which form theframe or field, wherein the encoding unit adds first informationindicating the first encryption method which is used in the first lineto the first line and adds second information indicating the secondencryption method which is used in the second line to the second line,wherein at least one of the encryption unit and the encoding unit isimplemented as a hardware component.
 9. A method for decrypting content,the method comprising: receiving a content stream which includesencrypted content and encryption information; and decrypting theencrypted content using a plurality of different decrypting schemes onportions of the encrypted content, wherein the one of the plurality ofdifferent decrypting schemes used is selected based on the encryptioninformation, wherein the encrypted content is encrypted after anauthentication to a connected apparatus succeeds, wherein a singlecontent comprises a plurality of frames, each frame comprises aplurality of fields, and each frame or each field comprises a pluralityof lines, wherein the encrypted content is encrypted by applying a firstencryption method to a first line and a second encryption method to asecond line through the remaining lines among the lines which form theframe or field, wherein first information indicating the firstencryption method which is used in the first line is added to the firstline and second information indicating the second encryption methodwhich is used in the second line is added to the second line.
 10. Themethod as claimed in claim 9, wherein the decrypting comprises complexlyapplying the selected ones of the plurality of different decryptingschemes on at least one of a per-frame basis, a per-field basis, and aper-line basis.
 11. The method as claimed in claim 10, wherein theplurality of different decrypting schemes comprise an HDCP-XORdecrypting scheme and an HDCP -XNOR decrypting scheme.
 12. The method asclaimed in claim 10, wherein: 1) the encryption information is referredto every frame when the encrypted content is decrypted on the per-framebasis, 2) the encryption information is referred to every field when theencrypted content is decrypted on the per-field basis, and 3) theencryption information is referred to every line when the encryptedcontent is decrypted on the per-line basis.
 13. An electronic apparatuscomprising: a communication unit which receives a content streamcomprising encryption information and encrypted content; a decryptionunit which decrypts the encrypted content using a plurality of differentdecrypting schemes on portions of the encrypted content; and acontroller which controls the decryption unit with reference to theencryption information so as to carry out selected ones of the pluralityof different decrypting schemes in accordance with the encryptioninformation, wherein the decryption unit decrypts the encrypted contentwhich is encrypted after an authentication to a connected apparatussucceeds, wherein a single content comprises a plurality of frames, eachframe comprises a plurality of fields, and each frame or each fieldcomprises a plurality of lines, wherein the decryption unit decrypts theencryped content which is encrypted by applying a first encryptionmethod to a first line and a second encryption method to a second linethrough the remaining lines among the lines which form the frame orfield, wherein the decryption unit decrypts the encrypted content inwhich first information indicating the first encryption method which isused in the first line is added to the first line and second informationindicating the second encryption method which is used in the second lineis added to the second line, wherein at least one of the communicationunit, the decryption unit, and the controller is implemented as ahardware component.
 14. A content playing device, comprising: acontroller that controls a communication unit, a decoding unit, adecryption unit, and an output unit; wherein: the communication unitreceives a content stream; the decoding unit extracts encrypted contentand encryption information from the content stream; the control unituses the encryption information to control the decryption unit indecrypting the encrypted content so as to produce unencrypted content;and the output unit outputs the unencrypted content, wherein thedecoding unit extracts the encrypted content which is encrypted after anauthentication to a connected apparatus succeeds, wherein a singlecontent comprises a plurality of frames, each frame comprises aplurality of fields, and each frame or each field comprises a pluralityof lines, wherein the decoding unit extracts the encrypted contentdecrypts which is encrypted by applying a first encryption method to afirst line and a second encryption method to a second line through theremaining lines among the lines which form the frame or field, whereinthe decoding unit extracts the encrypted content in which firstinformation indicating the first encryption method which is used in thefirst line is added to the first line and second information indicatingthe second encryption method which is used in the second line is addedto the second line, wherein at least one of the controller, thecommunication unit, the decoding unit, the control unit, and the outputunit is implemented as a hardware component.
 15. The content playingdevice as set forth in claim 14, wherein the encryption informationindicates one of at least two different encryption schemes to be used ondifferent portions of the encrypted content.
 16. The content playingdevice as set forth in claim 15, wherein the different portions of theencrypted content are different content frames.
 17. The content playingdevice as set forth in claim 15, wherein the different portions of theencrypted content are different content fields.
 18. The content playingdevice as set forth in claim 15, wherein the different portions of theencrypted content are different content lines.